Light-scattering and light-absorption based optical spectroscopy and imaging are powerful analytical and detection tools that have applied in pharmaceutical, material, chemical, biomedical, and a wide variety of other applications. The scattering and absorption processes occurring between light and matter can be elastic (e.g. Rayleigh scattering, infrared absorption, etc.) or inelastic (e.g. fluorescence scattering, Raman scattering, etc.). In an elastic process, the energy (i.e. the wavelength) of the incident photon is conserved to render the scattered photon with an identical wavelength, and only the direction of the scattered photon is changed. In an inelastic process, the incident photon interacts with matter and the frequency of the scattered photon is shifted to red or blue. A red shift occurs when part of the energy of the incident photon is transferred to the interacting matter, whilst the blue shift occurs when internal energy of the matter is transferred to the incident photon. Absorption occurs when the entire energy of the incident photon is transferred to the interacting matter and the photon annihilates.
Raman spectroscopy is an optical spectroscopic technique based on inelastic scattering of monochromatic light that can provide molecular information for specimens via probing vibrational energy transitions in molecules. In the Raman scattering process, molecules scatter photons, altering the photons' energy with energy quanta that are equivalent to the molecules' vibrational eigen-energies. Thus, Raman spectroscopy detects molecular vibrations of specimens. Raman spectroscopy can potentially be employed for in vitro and in vivo diagnosis of diseases and malignancies, in various tissues (e.g. lung, breast, prostate, ovarian, brain, bone and etc.), originating from biochemical differences between normal and diseased/malignant tissues. Because Ramen spectroscopy can provide information about molecular structure and composition of specimens with no contrast agents, Raman spectroscopy offers valuable complimentary information to current anatomical or functional imaging techniques such as electrochemical, electrical, thermal, ultrasound, X-ray and nuclear magnetic resonance (NMR).